This happens after updating to Windows 7 Service Pack 1. Memory leaks can happen when the background service for Windows Update (netsvcs) is enabled. You can find more info here, among other places. See Awa's answer here to verify that Windows Update is at fault.
One inelegant solution to this issue is to turn off Windows Update and install all updates manually. Run services.msc and set Windows Update and Background Intelligent Transfer Service to Disabled. See here for general instructions on services.
However, several updates to fix this issue have been rolled out by Microsoft. When you first run Windows Update in a new installation of Win7 SP1, it will insist on installing Windows Update Agent [WUA] 7.6.7600.320 (KB2887535), before it lets you check for other updates. Let it do so or apply the update manually if installing offline. After doing so, you might not be able to install other updates automatically until this issue is resolved.
Then, manually download and install the following update:
This updates the Windows Update Agent to version 7.6.7601.18979.
This is the newest update in a series released by Microsoft to address the issue. Each has been replaced by a newer version, and it seems that you only need to install the newest one. However, if this does not fix the issue, you can try installing an older update in the series, or perhaps install them all sequentially. In chronological order, consult the following updates:
https://support.microsoft.com/en-us/kb/3050265 (June 2015)
https://support.microsoft.com/en-us/kb/3065987 (July 2015)
https://support.microsoft.com/en-us/kb/3075851 (August 2015)
https://support.microsoft.com/en-us/kb/3083324 (September 2015)
Then, according to this answer, install this update:
This updates the WUA to version 7.6.7601.19046. Theoretically, you should be able to just skip to this step and be fine. However, this update claims to not replace earlier updates, which is why it might be advisable to install the aforementioned update(s) first.
Lastly, it might be advisable to disable the two aforementioned services before manually installing these updates, then re-enable them afterwards. I think you should be fine either way, though you might want to restart your machine after each update, just to be sure.
Reports vary, but this should fix your troubles with Windows Update hogging memory and CPU :)